Difference between revisions of "Using an Accumulator"

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(Using an accumulator to find the maximum.)
(Using an accumulator to concatenate.)
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<question className="P" title="Using an accumulator to concatenate.">
 
<question className="P" title="Using an accumulator to concatenate.">
 
<shell lang="java" className="P" import="shells.xml#main"/>
 
<shell lang="java" className="P" import="shells.xml#main"/>
<blurb>
+
<p class='imper'>Concatenate all items in the list</p>
<ul>
+
Notice that we are using a list of strings this time.
<li> We initialise to "". </li>
+
*We initialise to the empty string "".
<li> We concatenate the next value.  </li>
+
*We concatenate the next value (stick at the end).
<li> Each time i gets converted to a string and is put at the end.
+
</li>
+
<li>The answer is ""+2+7+1+1</li>
+
</ul>
+
</blurb>
+
 
<prog lang="java">
 
<prog lang="java">
 
String acc = "";
 
String acc = "";
for (int i : new int[]{2,7,1,1})
+
for (String s : new String[]{"two","seven","one","one"})
 
{
 
{
   acc += i;
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   acc += s;
 
}
 
}
 
System.out.println(acc);
 
System.out.println(acc);
 
</prog>
 
</prog>
 
</question>
 
</question>
 +
 
==Using two accumulators to find the mean.==
 
==Using two accumulators to find the mean.==
 
<question className="P" title="Using two accumulators to find the mean.">
 
<question className="P" title="Using two accumulators to find the mean.">

Revision as of 00:19, 8 December 2007

When using an accumulating variable there are three stages:

Initialise
We declare our accumulator and set it to an initial values.
Update
Inside the loop we update the accumulator - we take into account the current data item.
Output/use
After the loop our accumulator contains the required value. We use it or output it.

Using an accumulator to add.

Print the total of all of the numbers

  • We initialise to 0.
  • We add to the accumulator.
  • The value printed is the sum 0+2+7+1+1.


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Using an accumulator to count.

Print the number of items in the list.

  • We initialise to 0.
  • We increment the accumulator.
  • The value printed is the count: 0+1+1+1+1.


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Using an accumulator to count on a condition.

Count the number of 1s in the list

  • We initialise to 0.
  • We increment the accumulator only if the current value equals 1.


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Using an accumulator to multiply.

Print the product of the numbers.

  • We initialise to 1. (If you initialise to 0 then the result will always be 0.)
  • We multiply the accumulator.
  • The value printed is the product: 1*2*7*1*1


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Using an accumulator to find the maximum.

Print the largest number in the list.

  • We initialise to 0.
  • We take the max.
  • The value printed is the largest:

At each stage the accumulator stays the same or gets bigger (set to the current value).

max(max(max(max(0,2),7),1),1)


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Using an accumulator to concatenate.

Concatenate all items in the list

Notice that we are using a list of strings this time.

  • We initialise to the empty string "".
  • We concatenate the next value (stick at the end).


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Using two accumulators to find the mean.


  • We initialise both to 0.
  • We add to the sum and increment the count.
  • We divide the sum by the count to get the average.


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Using an accumulator to calculate.


  • We initialise to 0.
  • We multiply by the radix and add the next digit.
  • By the end the number 2 has been multiplied by 10 three times, the number has been multiplied by 10 twice...
  • 10*(10*(10*2+7)+1)+1


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